Stable hydrogen and oxygen isotope abundance analysis of barley malt and its potential to trace the malting location

The complexity of global food supply chains has driven demand for analytical tools that support traceability assessments beyond traditional documentation and routine quality control, as increasingly required by food safety standards. This also applies to the brewing industry, where important processing steps such as malting are often outsourced to third parties. To ensure full process transparency, breweries currently lack analytical solutions to verify that the barley supplied for malting was processed at the specified malthouse. In this study, stable hydrogen (δ2H) and oxygen (δ18O) isotope abundance analysis was applied to assess whether malting introduces location-related isotope signatures that could support origin verification. Thirty-four barley samples were analysed as raw barley and after parallel malting at two geographically separated German malthouses in Berlin and Munich using high-temperature conversion isotope-ratio mass spectrometry, resulting in three samples per barley lot and a total of 102 samples. Malting resulted in significant enrichments of both δ2H and δ18O values relative to the corresponding unmalted barley, indicating systematic isotopic fractionation during the malting process. In addition, malt samples produced at the two malthouses exhibited small but significant differences in hydrogen and oxygen isotope composition. The direction of these differences is consistent with regional patterns in precipitation isotope ratios and corresponding local brewing water sources. This study provides an analytical basis indicating that hydrogen and oxygen isotope ratios in malt reflect malting-location-related process information. When evaluated relative to supplied barley reference material, this approach can support plausibility-based malt traceability and could complement documentation-based verification.